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Connect Java to a MySQL database

开发者 https://www.devze.com 2022-12-30 14:43 出处：网络
How do you connect to a MySQL database in Java? When I try, I get java.sql.SQLException: No suitable driver found for jdbc:mysql://database/table
相关专题：

How do you connect to a MySQL database in Java?

When I try, I get 

java.sql.SQLException: No suitable driver found for jdbc:mysql://database/table
    at java.sql.DriverManager.getConnection(DriverManager.java:689)
    at java.sql.DriverManager.getConnection(DriverManager.java:247)

Or 

java.l开发者_Python百科ang.ClassNotFoundException: com.mysql.jdbc.Driver

Or

java.lang.ClassNotFoundException: com.mysql.cj.jdbc.Driver

Here's a step by step explanation how to install MySQL and JDBC and how to use it:

  1. Download and install the MySQL server. Just do it the usual way. Remember the port number whenever you've changed it. It's by default 3306.

  2. Download the JDBC driver and put in classpath, extract the ZIP file and put the containing JAR file in the classpath. The vendor-specific JDBC driver is a concrete implementation of the JDBC API (tutorial here).

    If you're using an IDE like Eclipse or Netbeans, then you can add it to the classpath by adding the JAR file as Library to the Build Path in project's properties.

    If you're doing it "plain vanilla" in the command console, then you need to specify the path to the JAR file in the -cp or -classpath argument when executing your Java application.

    java -cp .;/path/to/mysql-connector.jar com.example.YourClass

    The . is just there to add the current directory to the classpath as well so that it can locate com.example.YourClass and the ; is the classpath separator as it is in Windows. In Unix and clones : should be used.

  3. Create a database in MySQL. Let's create a database javabase. You of course want World Domination, so let's use UTF-8 as well.

     CREATE DATABASE javabase DEFAULT CHARACTER SET utf8 COLLATE utf8_unicode_ci;

  4. Create a user for Java and grant it access. Simply because using root is a bad practice.

     CREATE USER 'java'@'localhost' IDENTIFIED BY 'password';
 GRANT ALL ON javabase.* TO 'java'@'localhost' IDENTIFIED BY 'password';

    Yes, java is the username and password is the password here.

  5. Determine the JDBC URL. To connect the MySQL database using Java you need an JDBC URL in the following syntax:

    jdbc:mysql://hostname:port/databasename

    • hostname: The hostname where MySQL server is installed. If it's installed at the same machine where you run the Java code, then you can just use localhost. It can also be an IP address like 127.0.0.1. If you encounter connectivity problems and using 127.0.0.1 instead of localhost solved it, then you've a problem in your network/DNS/hosts config.

    • port: The TCP/IP port where MySQL server listens on. This is by default 3306.

    • databasename: The name of the database you'd like to connect to. That's javabase.

    So the final URL should look like:

    jdbc:mysql://localhost:3306/javabase

  6. Test the connection to MySQL using Java. Create a simple Java class with a main() method to test the connection.

     String url = "jdbc:mysql://localhost:3306/javabase";
 String username = "java";
 String password = "password";

 System.out.println("Connecting database...");

 try (Connection connection = DriverManager.getConnection(url, username, password)) {
     System.out.println("Database connected!");
 } catch (SQLException e) {
     throw new IllegalStateException("Cannot connect the database!", e);
 }

    If you get a SQLException: No suitable driver, then it means that either the JDBC driver wasn't autoloaded at all or that the JDBC URL is wrong (i.e. it wasn't recognized by any of the loaded drivers). Normally, a JDBC 4.0 driver should be autoloaded when you just drop it in runtime classpath. To exclude one and other, you can always manually load it as below:

     System.out.println("Loading driver...");

 try {
     Class.forName("com.mysql.jdbc.Driver");
     System.out.println("Driver loaded!");
 } catch (ClassNotFoundException e) {
     throw new IllegalStateException("Cannot find the driver in the classpath!", e);
 }

    Note that the newInstance() call is not needed here. It's just to fix the old and buggy org.gjt.mm.mysql.Driver. Explanation here. If this line throws ClassNotFoundException, then the JAR file containing the JDBC driver class is simply not been placed in the classpath.

    Note that you don't need to load the driver everytime before connecting. Just only once during application startup is enough.

    If you get a SQLException: Connection refused or Connection timed out or a MySQL specific CommunicationsException: Communications link failure, then it means that the DB isn't reachable at all. This can have one or more of the following causes:

    1. IP address or hostname in JDBC URL is wrong.
    2. Hostname in JDBC URL is not recognized by local DNS server.
    3. Port number is missing or wrong in JDBC URL.
    4. DB server is down.
    5. DB server doesn't accept TCP/IP connections.
    6. DB server has run out of connections.
    7. Something in between Java and DB is blocking connections, e.g. a firewall or proxy.

    To solve the one or the other, follow the following advices:

    1. Verify and test them with ping.
    2. Refresh DNS or use IP address in JDBC URL instead.
    3. Verify it based on my.cnf of MySQL DB.
    4. Start the DB.
    5. Verify if mysqld is started without the --skip-networking option.
    6. Restart the DB and fix your code accordingly that it closes connections in finally.
    7. Disable firewall and/or configure firewall/proxy to allow/forward the port.

    Note that closing the Connection is extremely important. If you don't close connections and keep getting a lot of them in a short time, then the database may run out of connections and your application may break. Always acquire the Connection in a try-with-resources statement. Or if you're not on Java 7 yet, explicitly close it in finally of a try-finally block. Closing in finally is just to ensure that it get closed as well in case of an exception. This also applies to Statement, PreparedStatement and ResultSet.

That was it as far the connectivity concerns. You can find here a more advanced tutorial how to load and store fullworthy Java model objects in a database with help of a basic DAO class.

Using a Singleton Pattern for the DB connection is a bad approach. See among other questions: Is it safe to use a static java.sql.Connection instance in a multithreaded system?. This is a #1 starters mistake.

DriverManager is a fairly old way of doing things. The better way is to get a DataSource, either by looking one up that your app server container already configured for you:

Context context = new InitialContext();
DataSource dataSource = (DataSource) context.lookup("java:comp/env/jdbc/myDB");

or instantiating and configuring one from your database driver directly:

MysqlDataSource dataSource = new MysqlDataSource();
dataSource.setUser("scott");
dataSource.setPassword("tiger");
dataSource.setServerName("myDBHost.example.org");

and then obtain connections from it, same as above:

Connection conn = dataSource.getConnection();
Statement stmt = conn.createStatement();
ResultSet rs = stmt.executeQuery("SELECT ID FROM USERS");
...
rs.close();
stmt.close();
conn.close();

Initialize database constants

Create constant properties database username, password, URL and drivers, polling limit etc.

// init database constants
// com.mysql.jdbc.Driver
private static final String DATABASE_DRIVER = "com.mysql.cj.jdbc.Driver";
private static final String DATABASE_URL = "jdbc:mysql://localhost:3306/database_name";
private static final String USERNAME = "root";
private static final String PASSWORD = "";
private static final String MAX_POOL = "250"; // set your own limit

Initialize Connection and Properties

Once the connection is established, it is better to store for reuse purpose.

// init connection object
private Connection connection;
// init properties object
private Properties properties;

Create Properties

The properties object hold the connection information, check if it is already set.

// create properties
private Properties getProperties() {
    if (properties == null) {
        properties = new Properties();
        properties.setProperty("user", USERNAME);
        properties.setProperty("password", PASSWORD);
        properties.setProperty("MaxPooledStatements", MAX_POOL);
    }
    return properties;
}

Connect the Database

Now connect to database using the constants and properties initialized.

// connect database
public Connection connect() {
    if (connection == null) {
        try {
            Class.forName(DATABASE_DRIVER);
            connection = DriverManager.getConnection(DATABASE_URL, getProperties());
        } catch (ClassNotFoundException | SQLException e) {
            // Java 7+
            e.printStackTrace();
        }
    }
    return connection;
}

Disconnect the database

Once you are done with database operations, just close the connection.

// disconnect database
public void disconnect() {
    if (connection != null) {
        try {
            connection.close();
            connection = null;
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

Everything together

Use this class MysqlConnect directly after changing database_name, username and password etc.

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.Properties;

public class MysqlConnect {
    // init database constants
    private static final String DATABASE_DRIVER = "com.mysql.cj.jdbc.Driver";
    private static final String DATABASE_URL = "jdbc:mysql://localhost:3306/database_name";
    private static final String USERNAME = "root";
    private static final String PASSWORD = "";
    private static final String MAX_POOL = "250";

    // init connection object
    private Connection connection;
    // init properties object
    private Properties properties;

    // create properties
    private Properties getProperties() {
        if (properties == null) {
            properties = new Properties();
            properties.setProperty("user", USERNAME);
            properties.setProperty("password", PASSWORD);
            properties.setProperty("MaxPooledStatements", MAX_POOL);
        }
        return properties;
    }

    // connect database
    public Connection connect() {
        if (connection == null) {
            try {
                Class.forName(DATABASE_DRIVER);
                connection = DriverManager.getConnection(DATABASE_URL, getProperties());
            } catch (ClassNotFoundException | SQLException e) {
                e.printStackTrace();
            }
        }
        return connection;
    }

    // disconnect database
    public void disconnect() {
        if (connection != null) {
            try {
                connection.close();
                connection = null;
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
}

How to Use?

Initialize the database class.

// !_ note _! this is just init
// it will not create a connection
MysqlConnect mysqlConnect = new MysqlConnect();

Somewhere else in your code ...

String sql = "SELECT * FROM `stackoverflow`";
try {
    PreparedStatement statement = mysqlConnect.connect().prepareStatement(sql);
    ... go on ...
    ... go on ...
    ... DONE ....
} catch (SQLException e) {
    e.printStackTrace();
} finally {
    mysqlConnect.disconnect();
}

This is all :) If anything to improve edit it! Hope this is helpful.

String url = "jdbc:mysql://127.0.0.1:3306/yourdatabase";
String user = "username";
String password = "password";

// Load the Connector/J driver
Class.forName("com.mysql.jdbc.Driver").newInstance();
// Establish connection to MySQL
Connection conn = DriverManager.getConnection(url, user, password);

Here's the very minimum you need to get data out of a MySQL database:

Class.forName("com.mysql.jdbc.Driver").newInstance();
Connection conn = DriverManager.getConnection
   ("jdbc:mysql://localhost:3306/foo", "root", "password");

Statement stmt = conn.createStatement();
stmt.execute("SELECT * FROM `FOO.BAR`");
stmt.close();
conn.close();

Add exception handling, configuration etc. to taste.

you need to have mysql connector jar in your classpath.

in Java JDBC API makes everything with databases. using JDBC we can write Java applications to
1. Send queries or update SQL to DB(any relational Database) 2. Retrieve and process the results from DB

with below three steps we can able to retrieve data from any Database

Connection con = DriverManager.getConnection(
                     "jdbc:myDriver:DatabaseName",
                     dBuserName,
                     dBuserPassword);

Statement stmt = con.createStatement();
ResultSet rs = stmt.executeQuery("SELECT a, b, c FROM Table");

while (rs.next()) {
    int x = rs.getInt("a");
    String s = rs.getString("b");
    float f = rs.getFloat("c");
}

You can see all steps to connect MySQL database from Java application here. For other database, you just need to change the driver in first step only. Please make sure that you provide right path to database and correct username and password.

Visit http://apekshit.com/t/51/Steps-to-connect-Database-using-JAVA

MySQL JDBC Connection with useSSL. 

private String db_server = BaseMethods.getSystemData("db_server");
private String db_user = BaseMethods.getSystemData("db_user");
private String db_password = BaseMethods.getSystemData("db_password");

private String connectToDb() throws Exception {
   String jdbcDriver = "com.mysql.jdbc.Driver";
   String dbUrl = "jdbc:mysql://" + db_server  +
        "?verifyServerCertificate=false" +
        "&useSSL=true" +
        "&requireSSL=true";
    System.setProperty(jdbcDriver, "");
    Class.forName(jdbcDriver).newInstance();

    Connection conn = DriverManager.getConnection(dbUrl, db_user, db_password);
    Statement statement = conn.createStatement();
    String query = "SELECT EXTERNAL_ID FROM offer_letter where ID =" + "\"" + letterID + "\"";
    ResultSet resultSet = statement.executeQuery(query);
    resultSet.next();
    return resultSet.getString(1);
}

Short and Sweet code.

try {       
    Class.forName("com.mysql.jdbc.Driver");
    System.out.println("Driver Loaded");
    conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/testDB","root","");
    //Database Name - testDB, Username - "root", Password - ""
    System.out.println("Connected...");         
} catch(Exception e) {
    e.printStackTrace();
}

For SQL server 2012

try {
    String url = "jdbc:sqlserver://KHILAN:1433;databaseName=testDB;user=Khilan;password=Tuxedo123"; 
    //KHILAN is Host    and 1433 is port number     
    Class.forName("com.microsoft.sqlserver.jdbc.SQLServerDriver");
    System.out.println("Driver Loaded");
    conn = DriverManager.getConnection(url);
    System.out.println("Connected...");
} catch(Exception e) {
    e.printStackTrace();
}

Connection I was using some time ago, it was looking like the easiest way, but also there were recommendation to make there if statement- exactly 

Connection con = DriverManager.getConnection(
                     "jdbc:myDriver:DatabaseName",
                     dBuserName,
                     dBuserPassword);
if (con != null){
 //..handle your code there 
}

Or something like in that way :)

Probably there's some case, while getConnection can return null :)

HOW
  • To set up the Driver to run a quick sample
1. Go to https://dev.mysql.com/downloads/connector/j/, get the latest version of Connector/J

2. Remember to set the classpath to include the path of the connector jar file.
If we don't set it correctly, below errors can occur:

No suitable driver found for jdbc:mysql://127.0.0.1:3306/msystem_development

java.lang.ClassNotFoundException: com.mysql.jdbc:Driver
  • To set up the CLASSPATH

Method 1: set the CLASSPATH variable.

export CLASSPATH=".:mysql-connector-java-VERSION.jar"
java MyClassFile

In the above command, I have set the CLASSPATH to the current folder and mysql-connector-java-VERSION.jar file. So when the java MyClassFile command executed, java application launcher will try to load all the Java class in CLASSPATH. And it found the Drive class => BOOM errors was gone.

Method 2:

java -cp .:mysql-connector-java-VERSION.jar MyClassFile

Note: Class.forName("com.mysql.jdbc.Driver"); This is deprecated at this moment 2019 Apr.

Hope this can help someone!

MySql JDBC Connection:

Class.forName("com.mysql.jdbc.Driver");     

Connection con=DriverManager.getConnection("jdbc:mysql://localhost:3306/DatabaseName","Username","Password");         
Statement stmt=con.createStatement();            
stmt = con.createStatement();
ResultSet rs=stmt.executeQuery("Select * from Table");

Short Code

public class DB {

    public static Connection c;

    public static Connection getConnection() throws Exception {
        if (c == null) {
            Class.forName("com.mysql.jdbc.Driver");
            c =DriverManager.getConnection("jdbc:mysql://localhost:3306/DATABASE", "USERNAME", "Password");
        }
        return c;
    }

    // Send data TO Database
    public static void setData(String sql) throws Exception {
        DB.getConnection().createStatement().executeUpdate(sql);
    }

    // Get Data From Database
    public static ResultSet getData(String sql) throws Exception {
        ResultSet rs = DB.getConnection().createStatement().executeQuery(sql);
        return rs;
    }
}

Download JDBC Driver

Download link (Select platform independent): https://dev.mysql.com/downloads/connector/j/

Move JDBC Driver to C Drive

Unzip the files and move to C:\ drive. Your driver path should be like C:\mysql-connector-java-8.0.19\mysql-connector-java-8.0.19

Run Your Java

java -cp "C:\mysql-connector-java-8.0.19\mysql-connector-java-8.0.19\mysql-connector-java-8.0.19.jar" testMySQL.java

testMySQL.java

import java.sql.*;
import java.io.*;

public class testMySQL {
    public static void main(String[] args) {
    // TODO Auto-generated method stub
        try
        {  
            Class.forName("com.mysql.cj.jdbc.Driver");  
            Connection con=DriverManager.getConnection(  
                "jdbc:mysql://localhost:3306/db?useSSL=false&useUnicode=true&useJDBCCompliantTimezoneShift=true&useLegacyDatetimeCode=false&serverTimezone=UTC","root","");  
            Statement stmt=con.createStatement();  
            ResultSet rs=stmt.executeQuery("show databases;");  
            System.out.println("Connected");  
        }
        catch(Exception e)
        {
            System.out.println(e);
        }

    }  

}

Connect Java to a MySQL database

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